There's a single buyer that wants a particular missile, and multiple defense contractors bidding on right to supply it. At some point hopefully before, but sometimes after the bid is won, that contractor has to figure out how to make and deliver that thing, which is a standard manufacturing process involving a bunch of components and subsystems, some of which are made in house, some of which are bought of the shelf, and some of which are outsourced. That part's the supply chain.

Oh, the idea of supply chains, and supply chain management make aboslute sense. Traditionally, logistics, and as an out grow of that supply chains, started with the military.

In the case of military goods, especially of the more expendable type like all kinds of ammunitions but also complex systems like tank or fighter jets, it is even harder since there is, in piece time at least, no continious demand. That means as soon as the large initial production runs are delivered, production capacity sits there unused. And gets ultimately dismanteled, technology becomes obsolete, people change jobs and retire.

All that is left at some point is maintenance capabilities, which only gets you that far in terms of building new gear, and low level production to replenish stores or conduct retrofits. Increasing that lost capacity is expensive and time consuming.

Generally, a supply chain is everything that has a supplier and a customer and moves physical goods. And the general, underlying principles haven't really changed since the days of the first silk road, or heck, since as early as the bronze age.

There are multiple buyers of most US weapon systems. For the FIM-92 (Stinger), there are over 30 not counting the US.